Hi @og, I’ve seen this before and for me it was an ambient resolution problem. You can plug the Ambient Resolution component into the additional_par_ input of the Radiance Parameter component.
It might also be worth considering how large your context is and if it’s really relevant - I think one of the reasons a higher -ar input is needed is due to the size of the model + context. The smaller your total model size the lower the -ar input needs to be. To find out more you might need to look on the Radiance forum, the pdf below by John Mardaljevic is also quite useful